To meet the increasing demands of high-bandwidth, high-speed mobile access, the Third Generation Partnership Projects (3GPP) puts forward a Long-Term Evolution Advanced (LTE-Advanced) standard. The LTE-Advanced maintains the core of the original LTE system, but has evolved to expand frequency domain and space domain through a series of technologies. The LTE-Advanced improves frequency spectrum utilization rate, increases system capacity, and the like. The Radio Relay technology is one of the technologies in the LTE-Advanced, which aims to expand cell coverage area, reduce communication uncovered area, balance load, forward services at hot spots, and save transmission power of User Equipment (UE), i.e., a terminal. As shown in FIG. 1, new RNs are added between an original base station (Donor-eNB) and UE. The RNs are connected with the base station over radio, wherein the radio links between the Donor-eNB and the RNs are called backhaul links, and the radio links between the RNs and the UE are called access links. Downlink data is transmitted first to the base station, then to the RNs, and finally to the UE, while uplink data is transmitted in a reverse order.
To configure the resources of the backhaul link, the Relay-node Physical Downlink Control Channel (R-PDCCH), Relay-node Physical Downlink Shared Channel (R-PDSCH) and Relay-node Physical Uplink Shared Channel (R-PUSCH) are defined. The R-PDCCH resources may be part of Physical Resource Blocks (PRB) in the subframe for the downlink transmission of the backhaul link, or they may be part or all of OFDM signals in the subframe for the downlink transmission of the backhaul link. A base station dynamically or semi-statically allocates R-PDSCH and R-PUSCH resources for an RN through the R-PDCCH, wherein the R-PDSCH resources are used for transmitting the downlink data of the backhaul link, and the R-PUSCH resources are used for transmitting the uplink data of the backhaul link. An RN can monitor the downlink assignment (i.e., PDSCH resources), uplink grant (i.e., PUCCH and/or PUSCH resources) and the like indicated by a base station on the PDCCH, and implement the data transmission between itself and the base station on the corresponding PDSCH and PUSCH. The RN can also monitor the downlink assignment (i.e., R-PDSCH resources), uplink grant and the like indicated by a base station on the R-PDCCH, and implements the transmission between itself and base station on the corresponding R-PDSCH and R-PUSCH. Moreover, the RN indicates the downlink assignment, uplink grant and the like on the PDCCH of an access link, and implements the transmission between itself and a UE on the corresponding PDSCH and PUSCH, so as to avoid the conflict between the transmission between itself and the base station and that between itself and the UE.
The RN can be in one of the following states:
Idle State:
The RN is in an idle state when is initially powered-on or after the radio links fail to be re-set up. When in an idle state, the RN has completely or partially same functions as that of a UE in an idle state, such as a system information acquisition function, a measurement function, a cell selection/reselection function and the like.
Connection State of Serving as a UE:
The RN has completely or partially the same functions as that of the UE in the connection state when in the connection state of serving as a UE, such as a system information acquisition function, a measurement function, a reporting function, a switching function, a function of transmitting data between a base station and an RN by a PDCCH and a PDSCH or PUSCH, and other functions. The RN does not have a relay function when in the connection state of serving as a UE, i.e., it is incapable of allowing a UE to access the network via RN.
Connection State of Enabling a Relay Function:
The RN has the relay function when in such state, i.e., it has the relay function of transmitting data between itself and the base station, and between itself and a UE managed thereby. Specifically, between the base station and the RN, the relay function includes a system information acquisition function, a measurement function, a measurement reporting function, a switching function, a function of transmitting data by an R-PDCCH and an R-PDSCH or R-PUSCH, and other functions. The RN can also manage cells belonging thereto, as well as UEs in the cells, when in the connection state of enabling a relay function. Between the RN and the UE, the relay function includes the functions of sending the system information of the RN, managing the measurement process and the switching process of the UE, transmitting data between the RN and the UE by a PDCCH and a PDSCH/PUSCH, and other functions.
The RN can switch from an idle state to the connection sate of the UE via a radio resource control (RRC) connection setup process, and can switch from the connection state of serving as a UE to the idle state via an RRC connection releasing process.
The state accessing process of the RN includes the following contents:
(1) After the RN is initially power-on, cell search is implemented, and a cell in the Donor-eNB is selected to read the system information thereof, wherein the RN is in an idle state at that moment. The main function of the RN is to provide services for the UEs within its coverage area, so the time when the RN is in an idle state is very short.
(2) The RN selects a random access preamble according to the random access resources in system information, initiates a random access, and sets up an RRC connection, and then a network side authenticates and encrypts the RN and configures a Data Radio Bearer (DRB) which is used for data transmission for the RN by RRC connection reconfiguration after the success of the authentication and the encryption. In the process, once the random access is initiated successfully, the RN is in the connection state of serving as a UE, and needs to monitor the PDCCH sent by the base station and detect its own PDCCH and/or the PDSCH in the same subframe according to the Radio Network Temporary Identifier (RNTI), including Cell RNTI, SPS RNTI and the like, allocated thereto by the base station. The RN can notify the base station of the information that what is accessed is the RN rather than an ordinary UE through an air interface signalling, and acquire the RN access information by the authentication of the RN through a core network or through an Operation & Maintenance (O&M) system.
(3) After the DRB is set up in the RN, the O&M system transmits configuration data to the RN so that the RN can perform the relay function and provide services for the UEs within its coverage area. The downloaded configuration data includes the parameter information for configuring its own system information by the RN, such as a tracking area code, a cell identity, and a cell selection/reselection parameter. The downloaded configuration data may also include the configuration parameters required by the RN in the connection state of enabling a relay function, such as R-PDCCH configuration information, R-PDSCH configuration information, R-PUSCH configuration information, the dedicated scheduling request configuration information for the RN, subframe information for scheduling the RN (corresponding to the fake MBSFN subframe of an access link), and specific identity of the RN. After acquiring such configuration information, the RN initiates the required parameters to prepare for providing cell services by the relay functions. The RN also initiates the related counters and state variables, as well as rationally configures the system information of the provided cells, and the like.
When the access link and the backhaul link share the same frequency band, on one hand, the RN must maintain connection (the uplink data exchange and downlink data exchange in the backhaul link) with a Donor-eNB, on the other hand, it must maintain connection (the uplink data exchange and downlink data exchange in the access link) with a UE, thus creating a conflict in the processing of the RN. To resolve the conflict, a Fake Multicast Broadcast Single Frequency Network (Fake MBSFN) subframe is introduced. In the Fake MBSFN subframe, the RN exchanges data with the base station without sending a signal to a UE in the access link, and broadcasts the Fake MBSFN subframe information so that the UE does not monitor signals transmitted by the RN in the subframe. When the RN is in the connection state of enabling a relay function within the Fake MBSFN subframe, the base station schedules the RN through the R-PDCCH, but there is no effective solution in the prior art for how to actively change the RN from the initial connection state of serving as a UE to a normal working state (or the connection state of enabling a relay function). One simple solution is that the base station specially controls the state changes of the RN via a dedicated signalling. However, such solution requires the modification on the interface signalling of the existing protocol, and also fails to consider the processing time delay in the local parameters configuration of the RN, so it is necessary to provide a new solution.